1. Field of the Invention
This invention relates to hot water heaters and more particularly, to a two-stage electric hot water heater which is characterized by a tank having a vertically-oriented flue pipe in the center thereof and multiple heating elements encased in copper tubes extending through the flue pipe for heating water in the tank surrounding the flue pipe. In a first preferred embodiment a single-stage or two-stage thermostat is utilized to energize the heating elements, raise the water temperature to a specified level and maintain the water temperature at this level. In a second preferred embodiment a single-stage thermostat is provided in the circuit with a two-stage thermostat to maintain the water at a selected temperature. In the second embodiment the two-stage thermostat is wired in the circuit with tile heating elements to facilitate energizing of selected ones of the heating elements for quickly heating the water in the tank at a high energy level and subsequently switching maintenance of the water temperature to the single-stage thermostat when the water reaches a selected maintenance temperature. In a most preferred embodiment of the invention the heating elements are extended upwardly through selected ones of a cluster of copper tubes provided in the flue pipe and downwardly through other selected copper tubes. The ends of the heating elements are attached electrically to the two-stage thermostat and, in the case of the second embodiment of the invention, also to the single-stage thermostat, for operation. A resettable limit switch may also be provided in the circuit, as desired. Furthermore, the copper tubes which receive the heating elements may be dimpled or crimped to engage the heating elements in spaced relationship along the length of the heating elements, in order to increase heat transfer by conduction. Moreover, a quantity of junk copper may be stacked on top of the bends in the heating elements and the tubing cluster to provide a heat sink and further increase heat transfer to the water enclosed in the tank.
One of the problems which exists in electric water heaters is the high cost of heating water in the tank to a selected temperature and maintaining the water at this temperature for extended periods of time. This problem is exacerbated under circumstances where high demands are made on the water heater and the electric heating elements must be energized almost constantly to meet the demand. Various types of electric heating elements, including immersion-type elements and enclosed heating elements, have-been used in the past and with the development of the former, a serious problem of heat transfer reduction by scale and sediment is presented. This scaling and corrosion significantly reduces the efficiency of the elements and causes frequent burn-outs.
It has been long known that maintaining water in a water heater tank at a high temperature is wasteful due to heat losses by conduction and convection, thereby requiring significant thickness of insulation in the tanks to minimize this loss. Maintaining the water at such a high temperature also promotes more rapid wear and tear, particularly on the heating elements, but also on the water heater tank itself. Accordingly, thermostatic controls are provided in these water heaters in order to control the water temperature in the tank and these controls provide an energy saving expedient for more efficient operation of electric water heaters.
An early "Water Heater" is detailed in U.S. Pat. No. 1,779,937, dated Oct. 28, 1930, to E. F. Holinger. The water heater includes a water holding tank having an opening in the top and an apparatus adapted to hold an electrically operated heating unit and distribute the heat therefrom. This apparatus is adapted for insertion through the opening as a unit and then attached to the tank for closing the opening. An "Electrical Heater for Tubular Boilers and Like Apparatus" is detailed in U.S. Pat. No. 1,986,636, dated Jan. 1, 1935, to E. F. Holinger. The Holinger device includes an electrical heating apparatus which can be safely inserted in the tubes of fire tube boilers and heat water in the boilers. The heater unit extends from either end of the boiler tube and the heating coil or electric resistor is contained in a perforated cylinder, which permits air circulation, but prevents the resistor from coming into contact with the boiler tube in case the latter sags or breaks. A "Dual Compartment Electric Water Heater" includes inner and outer water heating compartments in thermal communication with each other and arranged for free thermal communication of water therebetween. First and second electric elements are controlled by separate thermostats responsive to the water temperature in the tank. U.S. Pat. No. 4,474,139, dated Oct. 2, 1984, to John J. Dobias, details another "Water Heater Structure". The device includes an inner water tank into which cold water is passed and from which hot water is periodically withdrawn. It includes a jacket within the inner water tank constructed of material which absorbs and gives up heat rapidly, such that upon periodic withdrawal of hot water from the inner water tank, cold water entering the inner water tank is rapidly heated by the jacket, which has assumed the temperature of the hot water in the tank. A "Two-Stage Electric Water Heater" is detailed in U.S. Pat. No. 4,514,617, dated Apr. 30, 1985, to Haim Amit. The device includes a storage vessel and an elongated, thermostatically-controlled electric resistance heating element positioned in the vessel and surrounded by an elongated metal tube having a closed outer end attached to the wall of the vessel. The metal tube has an open inner end positioned at a higher level in the vessel and terminates short of the top of the vessel. The heater water outlet extends from the outer end of the tube to the outside of the vessel. An elongated, tubular, thermally-insulating body concentrically surrounds a major part of the length of the tube and is spaced from the tube to form a convective water flow passage communicating with the interior of the vessel near the inner and outer ends of the tube. During non-consumption, water flows upwardly through the water flow passage and is heated to a medium temperature by heat transfer from the metal tube, for storage in the vessel. During consumption, the stored water flow comes from the vessel end of the tube through the open end thereof and is heated to a high temperature by direct contact with the electric heater prior to discharge through the outlet for consumption. A "Combined Electric Heating and Water Inlet/Outlet Assembly for Water Heating Tanks" is detailed in U.S. Pat. No. 4,578,565, dated Mar. 25, 1986, to S. Dawidowwitch. The assembly is designed for installation in the bottom opening of a domestic water heater tank and includes a plastic mounting flange designed to cover the opening and a plastic, open-top, cylindrical sleeve extending upwardly therefrom and adapted to project into the tank through the opening. An electric immersion heating element is removably carried by the flange and projects into the sleeve and integrally-formed water inlet and outlet tubes extend along the outer generatixes of the sleeve. A second plastic, closed-top, cylindrical unit is received on top of the sleeve to form an extension thereof. An integral tubular section along the outer surface of the cylindrical members forms an extension of the outlet conduit and the closed top of the cylindrical member has an integral, upwardly-extending riser tube forming an outlet for water heated by the heating element. A series of integrally formed pairs of parallel, plastic tube lengths fit one on top of the other and on top of the tubular outlet and riser tube section to form extensions thereof up to the top wall of the tank. A valved opening is provided in the cylindrical member for introducing water from the tank and permitting termination of the water flow into the cylindrical member for replacing the heating element without emptying the whole tank.
It is an object of this invention to provide a two-stage electric hot water heater and control system which includes an elongated flue conduit located in a water tank and electric heating elements provided in elongated tubes located in the flue pipe for heating the tubes, flue conduit and the water surrounding the flue pipe to a selected temperature.
Another object of this invention is to provide an electric water heater provided with a two-stage thermostat and a single-stage thermostat and further including a tank fitted with an internal, vertically-oriented flue provided with a cluster of copper tubes and heating elements provided in selected ones of the copper tubes, which heating elements are wired to the two-stage and single-stage thermostats, wherein certain ones of the heating elements can be selectively energized to rapidly raise the water temperature in the tank and surrounding the flue pipe to a selected temperature and all of the heating elements may then be energized at a lower energy level to maintain the water at this selected temperature.
A still further object of this invention is to provide a new and improved electric hot water heater which is characterized by a cylindrical water-containing tank, a vertically-oriented flue pipe extending through the center of the tank and containing multiple, tightly clustered copper tubes, selected ones of which tubes contain electric heating elements, and two-stage and single-stage thermostats provided in series electrical connection with the heating elements, to facilitate selectively energizing certain ones of the heating elements by operation of the two-stage thermostat to rapidly heat water contained in the tank and surrounding the flue pipe to a selected temperature at a high energy level and switching the water temperature control function to the single-stage thermostat for energizing all electric heating elements at a lower energy level and maintaining water at this selected temperature.
Yet another object of this invention is to provide a two-stage electric hot water heater which is characterized by a cylindrical tank for containing water, a vertically-oriented flue pipe extending vertically through the center of the tank and containing multiple lengths of clustered copper tubing, wherein heating elements are extended upwardly through selected ones of the copper tubing and back downwardly through other selected ones of the copper tubing and still other lengths of the copper tubing serve as heat transfer filler pipe, and further including junk copper placed on top of the copper tubing and heating elements in the flue pipe as a heat sink, wherein a two-stage thermostat and a single-stage thermostat are attached in series with the heating elements to facilitate initially energizing selected ones of the heating elements at a high energy level to heat water contained in the tank to a selected temperature by operation of the two-stage thermostat and thereafter maintaining the water in the tank at this selected temperature at a lower energy level by heating all of the heating elements using the single-stage thermostat.
A still further object of this invention is to provide a new and improved two-stage electric hot water heater which utilizes a two-stage thermostat and a single-stage thermostat connected in series to electric heating elements located in copper tubes vertically oriented in the flue pipe of a hot water heater, with the copper tubes crimped or dimpled for contact with the enclosed heating elements to initially heat air in the tubes and then the tubes themselves, the flue pipe and water in the tank to a selected temperature by energizing selected ones of the heating elements through operation of the two-stage thermostat and subsequently maintaining the water at this temperature by operation of the single-stage thermostat.